This review evaluated the effects of cognitive remediation on cognitive performance, symptoms and functional outcomes in patients with schizophrenia. The authors concluded that cognitive performance was improved and smaller improvements were likely for functional outcomes when psychiatric rehabilitation was included. Unknown study quality and limited reporting of the review process made the reliability of the authors' conclusions unclear.

Authors' objectives

To evaluate the effects of cognitive remediation on cognitive functioning, symptoms and functional outcomes in patients with schizophrenia.

Searching

MEDLINE and PsychINFO were searched for published English-language articles for inclusion in the review. Search terms were reported.

Study selection

Randomised controlled trials (RCTs) of psychosocial interventions designed to improve cognitive functioning were eligible for inclusion in the review if 75% or more patients had schizophrenia, schizoaffective disorder or schizophreniform disorder. Outcomes had to be measured using at least one neuropsychological test aimed to reflect the generalisation of effects. Data had to be available or calculable for group means and standard deviations for baseline and post-intervention cognitive tests or statistics.

The included neuropsychological tests were categorised (by consensus of three reviewers) into the domains indicated by the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) consensus panel: attention/vigilance; speed of processing; verbal working memory; nonverbal working memory; verbal learning and memory; visual learning and memory; reasoning/problem solving; and social cognition.

More than half of the included participants were men and in-patients. Mean age was 36.3 years (range 15 to 47). A variety of computerised and non-computerised cognitive remediation programmes were included. Additional psychiatric rehabilitation elements were provided (largely to older participants) in a number of studies. Control groups received a range of active and passive interventions. The mean duration of cognitive remediation programmes was 12.8 weeks (range one to 104). The median number of hours ranged from 12.5 to 26. A large proportion of programmes contained a drill and practice intervention.

The authors stated neither how the papers were selected for the review nor how many reviewers performed the selection.

Assessment of study quality

The authors did not state that they assessed validity.

Data extraction

Data were extracted on post-treatment group means and standard deviations, pre-post difference scores or values for analysis of covariance (ANCOVA) and multivariate analysis of covariance (MANCOVA), in order to calculate the effect size and 95% confidence interval (CI). Effect sizes were classified as small (0.2), medium (0.5) or large (0.8). The mean effect size was calculated where data were reported from multiple measures within the same cognitive domain.

The authors stated neither how the data were extracted for the review nor how many reviewers performed the data extraction.

Methods of synthesis

Effect sizes (ES) and 95% CIs were pooled in a fixed-effect, or random-effects meta-analysis where significant heterogeneity was detected, and weighted by the inverse variance estimate. Heterogeneity was assessed using the Q statistic. Moderator analyses were conducted to explore the potential influence of participant age, setting, type of control group, type of intervention, hours of practice and whether adjunctive psychiatric rehabilitation had been provided.

Results of the review

Twenty-six studies (1,151 participants) were included in the review. Mean sample size was 50 (range 10 to 138).

There was statistically significant heterogeneity in the analysis for verbal learning and memory (p<0.05). Moderator analysis concluded that significantly larger effect sizes for this outcome were associated with more hours of cognitive remediation (ES 0.57, p<0.05) and for drill and practice interventions (ES 0.48, p<0.05) compared with drill and practice plus strategy coaching.

Statistically significant heterogeneity was found for functioning (p<0.01). Moderator analyses concluded that larger effect sizes for improved psychosocial functioning were found in studies where adjunctive psychiatric rehabilitation was offered (ES 0.47, p<0.01), where drill and practice plus strategy coaching was provided compared to drill and practice alone (ES 0.62, p<0.05) and in studies that included older participants (ES 0.55, p<0.05).

Authors' conclusions

A range of cognitive remediation programmes for schizophrenia can produce moderate improvements in cognitive performance. Functional outcomes were improved when additional psychiatric rehabilitation is provided.

CRD commentary

The review addressed a clear research question and was supported by potentially reproducible inclusion criteria. The search strategy appeared limited in its access to only two electronic databases and in its restriction to published English-language articles. This meant that relevant studies may have been missed and language and publication biases could not be ruled out.

There was no reported assessment of study quality. The absence of reporting of the review process represented a substantial threat to the reliability of the review findings. Details of the primary studies were adequately provided. Heterogeneity was appropriately explored. The chosen method of synthesis appeared suitable.

Due to concerns about unknown study quality and potential limitations in the review process, the extent to which the authors conclusions are reliable was unclear.

Implications of the review for practice and research

Practice: The authors did not state any implications for practice.

Research: The authors stated that further research was required to explore the effects of cognitive remediation in the longer term and on psychosocial function outcomes. Explorations of interactions between cognitive remediation and psychiatric rehabilitation and the mechanism of strategy coaching were recommended.

Funding

NIHM grant: MH77210. National Institute on Disability and Rehabilitation Research grant: H133G050230

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.